Low-temperature CO2 Methanation Research Articles

Doping Pd2+ into NinCeOx nanofibers promotes low-temperature CO2 methanation

CO2 methanation at low temperatures is still a challenge. Herein, NinCeOx (n = 1–3) and Ni2.5Pd0.1CeOx nanofibers by electrospinning is reported. The main advantage of this method is to obtain the highly dispersed precursor of palladium, nickel, and cerium, overcoming the difficulty of uniform mixing in conventional preparation methods. The Ni2.5Pd0.1CeOx nanofiber catalyst exhibited outstanding catalytic performance at low temperatures (CO2 conversion rate = 90.4 %, CH4 selectivity = 99.6 % at 230 °C) along with exceptional stability over 300 h. EPR, Raman, and O 1s XPS confirmed that Pd2+ doping increased oxygen vacancy concentration. In-situ infrared spectroscopy indicated that CO2 methanation on Ni2.5CeOx and Ni2.5Pd0.1CeOx catalysts followed the formate pathways. Pd2+ doping increased the number of surface oxygen vacancies and hydroxyl groups, thus increasing the amount of bicarbonates and formates. DFT calculations suggested that Pd2+ doping increased CO2 adsorption energy, and confirmed surface hydroxyl groups and bicarbonate being beneficial for CO2 methanation, consequently enhancing the activity of Ni2.5Pd0.1CeOx catalyst especially at low temperatures.

Molybdenum-doping promoted surface oxygen vacancy of CeO2 for enhanced low-temperature CO2 methanation over Ni-CeO2 catalysts

It is challenging to improve the low-temperature activity of Ni-based catalyst for the CO2 methanation reaction. In this study, a molybdenum-doped cerium oxide supported Ni catalyst (Ni/MoCe) was constructed, and it showed remarkable CO2 methanation performance at low temperatures (<300 °C). Structural analysis revealed that the incorporation of Mo into the CeO2 lattice could enrich the surface oxygen vacancies, reduce the particle size of Ni species and enhance the metal-support interaction. The Ni/MoCe demonstrated a faster HCOO* pathway for the conversion of CO2 to CH4 compared with Ni/CeO2. Besides, the rich surface oxygen vacancies in Ni/MoCe facilitated the adsorption form of bidentate carbonates and the enhanced Ni-CeO2 interaction reduced the approach resistance of active H species from Ni for subsequent hydrogenation process. This work proves that Mo doping is an effective vacancy engineering strategy to design high-performance heterogeneous catalysts for CO2 hydrogenation.

Optimizing Low-Temperature CO2 methanation with Aluminum-Doped Ni/CeO2 Catalysts: Insights into reaction pathway adjustments and strong Metal-Support interactions

Revealing the logical relationship between the structure, reaction mechanism and performance of the catalyst is a key step in the design of low-temperature CO2 methanation catalyst. The elemental Al was introduced into Ni/CeO2 using a co-precipitation method to form a composite support CeO2-Al2O3 loaded nickel-based catalyst. It was found that the incorporation of Al significantly improved the catalytic performance of low-temperature CO2 methanation. Notably, at a molar ratio of Al/Ce equal to 0.1, the catalyst exhibited optimal CO2 conversion of 88.83% and CH4 selectivity of 99.96% at 240 ℃. The addition of appropriate amounts of Al not only increases the specific surface area of the catalyst but also maintains a moderate strong interaction between metal Ni-support, thereby promoting the formation of active metal Ni species. Furthermore, the presence of Al leads to an increase in oxygen vacancy concentration, which facilitates the generation of numerous hydroxyl groups. Consequently, this alters the distribution of basic sites on the catalyst surface, resulting in a shift from the CO* pathway to a dual pathway involving both CO* and formate pathways. Remarkably, these divergent reaction pathways correspond to distinct active sites, thereby maximizing the utilization of each region within the catalyst. The diversity of reaction pathways and active sites represents pivotal factors for enhancing the catalytic performance of low-temperature CO2 methanation catalysts.

Enhanced CO2 methanation activity over Ni/CeO2 catalyst by adjusting metal-support interactions

CO2 methanation is an essential means of utilizing CO2, which is crucial to solving environmental problems and alleviating energy crisis. The design and development of high- performance low temperature CO2 methanation catalysts is the key to its further application. In this work, the metal-support interaction of Ni/CeO2 catalyst was regulated by changing the calcination temperature and Ni loadings to optimize the CO2 methanation performance. The results showed that 5NiCe-800 exhibited the best CO2 conversion of 83.1 % and 98.0 % CH4 selectivity at 350 °C, since it has a suitable Ni-CeO2 interaction, higher oxygen vacancy concentration, great reducibility and better basic site distribution. The reaction mechanism and the synergistic effect of CeO2 and Ni in CO2 methanation was revealed by in-situ FTIR, which is of great significance for the development of efficient CeO2 supported Ni-based for CO2 methanation.

Stabilization of the Active Ruthenium Oxycarbonate Phase for Low-Temperature CO2 Methanation.

Interstitial carbon-doped RuO2 catalyst with the newly reported ruthenium oxycarbonate phase is a key component for low-temperature CO2 methanation. However, a crucial factor is the stability of interstitial carbon atoms, which can cause catalyst deactivation when removed during the reaction. In this work, the stabilization mechanism of the ruthenium oxycarbonate active phase under reaction conditions is studied by combining advanced operando spectroscopic tools with catalytic studies. Three sequential processes: carbon diffusion, metal oxide reduction, and decomposition of the oxycarbonate phase and their influence by the reaction conditions, are discussed. We present how the reaction variables and catalyst composition can promote carbon diffusion, stabilizing the oxycarbonate catalytically active phase under steady-state reaction conditions and maintaining catalyst activity and stability over long operation times. In addition, insights into the reaction mechanism and a detailed analysis of the catalyst composition that identifies an adequate balance between the two phases, i.e., ruthenium oxycarbonate and ruthenium metal, are provided to ensure an optimum catalytic behavior.

Enhanced low-temperature CO2 methanation over La-promoted NiMgAl LDH derived catalyst: Fine-tuning La loading for an optimal performance

LDH-derived Ni-based catalysts are gathering momentum due to their excellent thermal stability but their low-temperature CO2 methanation is limited. In this study, various concentrations of La were introduced into the LDH-derived Ni-based catalysts for CO2 methanation, and the underlying mechanisms were investigated. The optimal Ni/La0.2-MgAlOx catalyst presented a CO2 conversion level of 69.0 % at 225 °C, which is over 7 times higher than that of conventional Ni/MgAlOx. The addition of small amounts of La could significantly enhance H spillover to promote the reduction of Ni species, but the oxygen vacancy concentration became the dominant factor causing changes in low-temperature activity as the La contents continue to increase. CO2 was found to be adsorbed at the oxygen vacancies in the form of bidentate carbonates, which are more reactive under an enhanced electron-rich environment. The research offers guidance to design effective and sustainable catalysts for low-temperature CO2 methanation.

Optimizing low-temperature CO2 methanation through frustrated Lewis pairs on Ni/CeO2 catalysts

The promising realm of carbon dioxide (CO2) conversion offers a compelling avenue to advance environmental sustainability. This study introduces a novel approach by utilizing frustrated Lewis pairs (FLPs) for efficient low-temperature CO2 methanation. Through a tailored ammonium bicarbonate (AB) precipitation method, we engineered Ni/CeO2 catalysts abundant in FLPs. Various morphologies, including aggregated flakes, broom-like structures, and irregular granules, were achieved by modulating the AB-to-cerium molar ratio. The distinctive broom-like Ni/(0.06AB)CeO2 catalyst, comprised of nanorods with abundant FLPs, exhibited outstanding low-temperature CO2 methanation performance: 67.5 % CO2 conversion, 99.6 % CH4 selectivity, and 0.27 s−1 CO2 turnover frequency (TOFCO2) at 240 °C, with excellent stability in a 100-h test at 300 °C. Furthermore, leveraging in-situ DRIFTS and in-situ Raman techniques, and DFT study, we unraveled CO2 hydrogenation pathways and found a dual interplay of CO and formate pathways in the low-temperature methanation over Ni/(0.06AB)CeO2 catalyst.

Lattice capacity-dependent activity for CO2 methanation: crafting Ni/CeO2 catalysts with outstanding performance at low temperatures.

In the pursuit of understanding lattice capacity threshold effects of oxide solid solutions for their supported Ni catalysts, a series of Ca2+-doped CeO2 solid solutions with 10 wt% Ni loading (named Ni/CaxCe1-xOy) was prepared using a sol-gel method and used for CO2 methanation. The lattice capacity of Ca2+ in the lattice of CeO2 was firstly determined by the XRD extrapolation method, corresponding to a Ca/(Ca + Ce) molar ratio of 11%. When the amount of Ca2+ in the CaxCe1-xOy supports was close to the CeO2 lattice capacity for Ca2+ incorporation, the obtained Ni/Ca0.1Ce0.9Oy catalyst possessed the optimal intrinsic activity for CO2 methanation. XPS, Raman spectroscopy, EPR and CO2-TPD analyses revealed the largest amount of highly active moderate-strength alkaline centers generated by oxygen vacancies. The catalytic reaction mechanisms were revealed using in situ IR analysis. The results clearly demonstrated that the structure and reactivity of the Ni/CaxCe1-xOy catalyst exhibited the lattice capacity threshold effect. The findings offer a new venue for developing highly efficient oxide-supported Ni catalysts for low-temperature CO2 methanation reaction and enabling efficient catalyst screening.

Ni-noble metal bimetallic catalysts for improved low temperature CO2 methanation

Bimetallic nickel-noble metal catalysts with low noble metal load (1 wt% of Ru, Pt, Rh, Pd, orIr) supported on Pr-doped CeO2 were comparatively evaluated regarding their CO2 methanation catalytic performance. Ru was the sole noble metal phase that could dramatically promote the catalytic activity of the corresponding monometallic catalyst, whereas the incorporation of the other noble metals either retained (Pt and Ir) or worsened (Rh and Pd) the catalytic performance. The best–performing RuNi bimetallic catalyst maintained around 80 % CO2 conversion and 99.5 % CH4 selectivity at 325 °C during 50 h of operation. Ru was found to be well dispersed along the support (as single atoms or small clusters), while a small part of it was also dispersed atop the medium-sized Ni nanoparticles. Its promoting ability was attributed to the improved metal dispersion, catalyst reducibility, moderate basicity and provision of additional active sites for CO2 and H2 dissociation, while DFT analysis evidenced that a Ru single atom atop a Ni cluster/ small particle is the structure that is most favorable towards the initial CO2 adsorption and dissociation.

Alkaline earth metal modified nickel nanoparticles supported on exfoliated g-C3N4 for atmospheric CO2 methanation

Alkaline earth metals such as magnesium (Mg) and calcium (Ca) are promising catalyst promoters for CO2 methanation owing to their exceptional basic characteristics. This study details the development of nickel-based catalysts promoted with Mg and Ca supported by exfoliated graphitic carbon nitride (eg-C3N4). The catalysts were synthesised using a facile impregnation technique and characterised using N2 physisorption, XRD, TEM, XPS, H2-TPR and CO2-TPD. The Mg-promoted catalyst showed a greater number of mesopores, better dispersion of small Ni NPs, stronger metal-support interaction and enhanced moderate basic sites compared to Ni/eg-C3N4. Conversely, the presence of bulk CaCO3 species in the Ca-doped catalyst negatively affected the textural properties and basicity. Ni-Mg/eg-C3N4 catalyst demonstrated superior methanation activity with CO2 conversion (XCO2) of 77% and CH4 selectivity (SCH4) greater than 99% at 322 °C. This is mainly attributed to the creation of a NiO-MgO solid solution which enhances the interaction between metal and support, leading to the promotion of small and highly dispersed Ni NPs. Moreover, the incorporation of an Mg promoter generates Lewis basic sites and alters the basicity of the eg-C3N4 support, increasing the number of effective CO2 adsorption sites. The synergy between the Mg dopant and eg-C3N4 support significantly contributes to the high activity and stability for low-temperature CO2 methanation.

Unveiling the promotion effect of ethylenediamine on preparation of Ni/CeO2 catalyst for low-temperature CO2 methanation

Cost-effective CO2 conversion to value-added products remains a great challenge until present. Here, we have discovered that the ethylenediamine (EDA) assisted preparation of Ni/CeO2 catalyst remarkably promotes the CO2 methanation performance at low temperatures. The Ni/CeO2-EDA catalyst exhibits a CO2 conversion efficiency of 84% and a CH4 selectivity of 98% at 225 °C, and no visible decline of CO2 conversion is observed even after 70h of continuous reaction. The involvement of EDA is shown to effectively result in a more uniform distribution of Ni species, coupled with a reduction in particle size. In addition, the smaller particle size of Ni results in a rapid dissociative adsorption of hydrogen and H2 spillover. Accordingly, oxygen vacancies on the CeO2 surface are created and adequate H atoms are engendered for CO2 hydrogenation. Furthermore, both the formate and CO pathways occur simultaneously on the Ni/CeO2-EDA catalyst, enhancing the low-temperature methanation activity. Herein, the EDA-assisted strategy provides an effective methodology in terms of well-dispersion and highly active catalysts for low-temperature CO2 methanation.

The construction of the Ni/La2O2CO3 nanorods catalysts with enhanced low-temperature CO2 methanation activities

In this work, the La(OH)3 nanorods were successfully synthesized by precisely regulating the parameters of the hydrothermal method. Then, a series of Ni-based CO2 methanation catalysts were fabricated via the incipient-wetness impregnation and deposition–precipitation methods by employing the La(OH)3 nanorods as the supports. The influences of the support morphology and the preparation method on the metal-support interaction, Ni dispersion, and the surface basicity were carefully investigated based on various techniques, such as XRD, SEM, H2-TPR, CO2-TPD, XPS, ect. It was found that the rod-shaped La(OH)3 supported catalyst prepared by the deposition–precipitation method performed the optimum activity and stability. The reason for this could be derived from the confinement effect of the crystal plane of the rod-shaped support, which would promote the formation of the strong metal-support interaction and the construction of the Ni-La interface with high activity. Furthermore, the online-tandem TG-MS and in-situ DRIFTS technologies were used to investigate the thermal decomposition performance of the catalyst precursors in the calcination process and the reaction intermediates of the CO2 methanation. Therefore, the fundamental roles of support morphology and catalyst preparation method were expected to direct the advancement of the Ni-based nanostructured catalysts with outstanding low-temperature performances.

An emerging and high-performance sepiolite-supported Ni catalyst for low-temperature CO2 methanation: The critical role of hydroxyl groups

Natural clay minerals compensate for the high cost, complex synthesis and environmental unfriendliness of conventional catalytic supports. To obtain highly-effective and stable clay mineral-supported Ni catalysts for CO2 methanation, 10 wt% Ni was loaded on five common clay minerals (sepiolite (Sep), attapulgite (ATP), montmorillonite (Mnt), diatomite (Dia) and halloysite (Hly)), SiO2 and Al2O3 with a simple impregnation method. 10 wt% Ni/Sep displayed the best catalytic activity, the highest turnover frequency (TOF) and excellent stability, due to the smallest Ni nanoparticles, the strongest weak and moderate basicity, the most abundant surface hydroxyl groups, electron transfer from Sep to Ni, and good resistance to sintering and carbon deposition. Meanwhile, correlation results indicated that hydroxyl groups of clay mineral catalysts are critical for CO2 methanation. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis revealed that magnesium in Sep demonstrates an outstanding ability to activate CO2 at room temperature and the reaction follows both CO and formate routes over 10 wt% Ni/Sep, where CO2 reacted with abundant hydroxyl groups to form bicarbonate; Then, the bicarbonate was further hydrogenated into formate or decomposed into CO, and finally the generation of CH4, which also explains the excellent catalytic performance of 10 wt% Ni/Sep, and deepens the understanding of CO2 methanation mechanism over clay mineral catalysts. This work provides a novel perspective regarding the natural character of clay minerals on CO2 methanation and facilitates the industrial application of high-performance sepiolite-supported Ni catalyst in CO2 methanation.

Graphene nanoplatelets promoted CoO-based catalyst for low temperature CO2 methanation reaction

Methanation of CO2 is an important reaction for reducing CO2 emissions in a power-to-gas system. Compared to cobalt supported on gamma-Al2O3, cobalt supported on graphene nanoplatelets (GNPs) showed significantly better performance for CO2 methanation. Cobalt supported on GNPs was capable of 15% conversion of CO2 to CH4 at temperatures below 250°C, compared to 5% for cobalt supported on Al2O3. In situ thermogravimetric analysis (TGA) demonstrated that the Co/GNP catalyst was stable to 400°C. The maximum catalyst mass-specific CH4 yield was obtained at a Co loading of 5wt% on GNPs; however, high Co loading on GNPs deactivated the reactivity of the Co/GNP catalyst. Transmission electron microscopy (TEM) demonstrated that 5wt% Co/GNPs had the smallest and most dispersed cobalt nanoparticles. Excessive loading of cobalt tended to form isolated large Co nanoparticles. X-ray photoelectron spectroscopy (XPS) and Raman spectrometry revealed that more CoO phases were maintained on the surface of 5wt% Co/GNPs, indicating that the interaction between the Co and the GNPs had more of an impact on cobalt’s redox capacity than did particle size, which ultimately affected cobalt’s active phase during the CO2 reduction process. Furthermore, Raman spectrometry demonstrated that Co loading led to an increase in graphene defects. Higher Co loading on GNPs resulted in fewer interfaces between Co and GNPs due to the agglomeration of Co nanoparticles.

An Active Manganese Promoted Ni/Al2O3 Catalyst for Low Temperature CO2 Methanation

An Active Manganese Promoted Ni/Al2O3 Catalyst for Low Temperature CO2 Methanation

Synergistic Catalysis at the Ni/ZrO2–x Interface toward Low-Temperature CO2 Methanation

The CO2 methanation reaction, which achieves the carbon cycle and gains value-added chemicals, has attracted much attention, but the design and exploitation of highly active catalysts remain a big challenge. Herein, zirconium dioxide-supported Ni catalysts toward low-temperature CO2 methanation are obtained via structural topological transformation of NiZrAl-layered double hydroxide (LDH) precursors, which have the feature of an interfacial structure (Ni-O-Zr3+-Vö) between Ni nanoparticles and ZrO2-x support (0 < x < 1). The optimized catalyst (Ni/ZrO2-x-S2) exhibits exceptional CO2 conversion (∼72%) at a temperature as low as 230 °C with a ∼100% selectivity to CH4, without obvious catalyst deactivation within a 110 h reaction at a high gas hourly space velocity of 30,000 mL·g-1·h-1. Markedly, the space-time yield of CH4 reaches up to ∼0.17 ·gcat-1·h-1, which is superior to previously reported Ni catalysts evaluated under similar reaction conditions. Both in situ/operando investigations (diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure) and catalytic evaluations substantiate the interfacial synergistic catalysis at the Ni/ZrO2-x interface: the Zr3+-Vö facilitates the activation adsorption of CO2, while the H2 molecule experiences dissociation at the metallic Ni sites. This work demonstrates that the metal-support interface effect plays a key role in improving the catalytic behavior toward CO2 methanation, which can be extended to other high-performance heterogeneous catalysts toward structure-sensitive systems.

Low-temperature CO2 methanation over Ru/CeO2: Investigation into Ru loadings

The in-depth study of reaction intermediates, especially metal-support interactions, has brought great promise and challenges to the application of Ru-based catalysts in CO2 methanation. In this study, catalysts with different Ru loadings were prepared by wet impregnation method using CeO2 as the support. It is found that 1%Ru/CeO2 had excellent low-temperature methanation activity compared with other catalysts. As the metal loading increases, the oxygen vacancy concentration of the catalyst shows a volcano-type trend and the metal-support interaction increases. In addition, in situ DRIFTS showed that the low-temperature conditions are conducive to the formation of CO intermediates, making the CO2 methanation pathway more inclined to proceed along the CO pathway; while high temperature conditions are conducive to the formation of HCOO* intermediates, making the CO2 methanation pathway more inclined to proceed along the HCOO* pathway. This study demonstrates the importance of precisely determining the influence of metal active sites on the interaction between metal supports and oxygen vacancies for identifying critical reaction pathway intermediates and predicting CO2 methanation performance.

Unveiling the potential of surfactant Pluronic-P123 application during the synthesis of Ni-hydrotalcite-derived catalysts for low-temperature CO2 methanation: A novel approach

For the tailoring purpose of NiMgAl-oxides (NMA) towards CO2 methanation, the surfactant Pluronic-P123 was first-time employed at different concentrations. Catalysts were examined by SEM-EDX, BET, XRD, H2-TPR, CO2-TPD, and TGA. By adding P123, a clear revolution in terms of the texture, morphology, and pore of catalysts was observed, which has never been recorded previously. The correlations between carbonate species and basic sites were identified thanks to in-situ CO2 sorption measurements. The stability of carbonate species was assumed to follow “hydrogen-carbonate < bidentate-carbonate < unidentate-carbonate < tridentate-carbonate”. On the activity stand, 3P-NMA exhibited ca. 83.5% CO2 conversion and 99.5% CH4 selectivity at 300 ℃ vs. 46% and 97%, respectively, for the base case (GHSV = 12,000 h−1, H2/CO2 = 4), alongside superior stability after a 16 h of TOS run. Furthermore, Operando FTIR data revealed the appearance of formyl (*HCO) species under methanation conditions, allowing us to propose the reaction mechanism following *HCO formation as the key intermediate for CO2 methanation.

Fabrication of highly active and stable Ni/CeO2-nanorods wash-coated on ceramic NZP structured catalysts for scaled-up CO2 methanation

The production of synthetic natural gas from CO2 methanation using green H2 produced via water electrolysis is a promising pathway regarding both the curtailment of excess power by variable renewables and the mitigation of CO2 emissions. Several catalytic systems have been employed for thermocatalytic CO2 methanation in lab-scale, with Ni-based catalysts being amongst the most cost-effective and active materials. In this regard, we have recently demonstrated the remarkable low-temperature CO2 methanation activity of a nickel catalyst supported on ceria nanorods, ascribed to the augmented metal-support synergy. Herein, we report on a scaled-up process of CO2 methanation, involving; i) fabrication of a highly porous NZP-type ceramic substrate of Ba1+xZr4P6–2xSi2xO24 in the form of extruded pellets, ii) wash-coating of Ni/CeO2-nanorods catalyst on NZP pellets, iii) design and testing of scaled-up experiments under a scaling factor of 80:1 and 65:1 in terms of mass and volume of catalysts compared to lab-scale experiments, respectively. The as-synthesized catalyst exhibited remarkable performance under variable reaction conditions and stable behavior after 75 h. Remarkably, the structured catalyst attained a methane formation rate of 277 NL gNi−1 h−1, being higher to numerous values reported in relevant works. Equally importantly, it was disclosed that increased values of space velocity led to high temperature gradient in the catalytic bed, thereby favoring the generation of CO. Intriguingly, the morphological and structural characteristics of the used catalyst remained unaltered even after various on/off reaction cycles and the stability test, which is a promising finding toward scaling-up the process at higher technology readiness levels using real feed streams.

Enhanced low-temperature CO2 methanation over Ni/ ZrO2-Al2O3 catalyst: Effect of Al addition on catalytic performance and reaction mechanism

It is desirable but challenging to obtain high CO2 conversion in low-temperature CO2 methanation and elucidate the reaction mechanism on nickel-based catalysts. In this work, we incorporated Al into Ni/ZrO2 to form nickel-based catalysts supported by ZrO2-Al2O3 composite support. The addition of the appropriate amount of Al increased the dispersion of metal Ni on the catalyst surface, promoted the activation and dissociation of H2, and thus significantly improved the activity of CO2 methanation at low-temperature (< 300 °C). The CO2 methanation on nickel-based catalysts supported on ZrO2-Al2O3 composite supports all follow the formate reaction pathway. Since adding Al removes the ability of ZrO2 to activate H2, the active sites of the catalyst change from the surrounding support to the support-Ni interface, which improves the efficiency of the hydrogenation reaction of the active intermediate.